A dragons breath in the Mists
Like a picture postcard of a vacation, when humanity began to put more faith in cold hard facts (and cold hard iron) over whim and fancy, the mythic parts of the world branched off to an overlapping level of reality called The Dreaming. Not quite Arcadia, it fit more with what both Fae and non-Fae felt that fairy-land should be.
Initially, this may have served as a buffer zone between Arcadia and the mundane world during the Sundering, connected to both by way of trods. When the Shattering took place, all paths to Arcadia itself were closed off and only the very rare path to the Dreaming remained. Fortunately this still allowed a slow trickle of Glamour to reach the mundane world. Only during the Resurgence were the trods between the Dreaming and the mundane world re-opened.
The Dreaming is better called “The Dreamings” (plural) since it is divided into three layers: The Near Dreaming, the Far Dreaming, and the Deep Dreaming.